1. Field of the Invention
The present invention relates generally to an optical fiber amplifier for use in optical fiber transmission systems, and more particularly to an optical passive component assembly constituting part of the optical fiber amplifier.
2. Description of the Prior Art
In optical fiber transmission systems, an optical fiber amplifier employing an erbium-doped optical fiber or fibers has widely been used wherein a plurality of optical passive components such as, for example, a polarized light coupler, an optical wavelength coupler (multiplexer), and a polarization-independent optical isolator are integrated. The polarized light coupler polarizes and couples two laser beams each having a wavelength of 1.48 .mu.m and emitted from two optically pumping laser diodes (semiconductor lasers), respectively, to obtain a doubled optical output. The optical wavelength coupler makes pumping light enter the erbium-doped optical fiber and takes out light having a wavelength of 1.55 .mu.m amplified by the erbium-doped optical fiber using an optical fiber. The polarization-independent optical isolator allows signal light to pass therethrough only in one direction, thereby preventing the amplified light from traveling in the reverse direction and entering the erbium-doped optical fiber again.
Each of these optical passive components generally includes at least two opposed lenses, two optical fibers disposed on opposite sides of the two opposed lenses, and various optical elements interposed therebetween. In applications where a plurality of optical passive components are integrated in an optical fiber amplifier, because the optical fiber amplifier requires a number of lenses, the size thereof becomes large and the manufacturing cost thereof becomes high. Furthermore, because optical fibers of one component are fused and connected to those of another, not only the optical loss is increased due to such connection, but also a variation in optical loss occurs. In addition, because each of conventional optical fiber amplifiers generally require space to fasten a number of optical passive components and space to place the mutually connected optical fibers, the amplifier body tends to become bulky.